1. Field of the Invention
This invention relates to an improved laser-energized heating probe having a temperature sensor at the distal end of an optical fiber and which is associated with a temperature control. The invention has particular utility in angioplasty procedures wherein tissue is heated for the recanalization of occluded blood vessels by removal of intravascular plaque and thrombi therefrom, as well as in other blood vessel and heating tissue treatments.
2. Description of the Related Art
Art related to the present invention is described in U.S. Pat. No. 4,760,845 and in copending U.S. patent application Ser. Nos. 180,188 (now U.S. Pat. 4,899,740), and 233,478 (now U.S. Pat. No. 4,890,898), which are incorporated by reference herein. Selected references from such art and their pertinent teachings are more fully described below by way of specific background to the present invention.
Aspects of the present invention concern an improved thermally conductive device and temperature sensing system for a laser-energized heating probe and which may be used as a modification of the laser systems described in the aforementioned U.S. Pat. No. 4,760,845 and copending U.S. applications Ser. Nos. 180,188 and 233,478. As discussed in these related patent applications and patent, occlusive heart disease involving blockage of vital coronary arteries is a major cause of death among persons in the adult population. The treatment of patients with occlusive arterial disease generally has been affected by two primary methods: pharmacological treatments for moderate arterial obstructions, and surgical treatments, including arterial bypass surgery and/or percutaneous transluminal angioplasty (PTA), in instances of severe stenosis. Although there are a number of advantages of PTA, a primary disadvantage of this treatment is that the material causing the arterial blockage such as arterial plaque or thrombi is not removed but only pushed aside, with the possibility of future occlusions resulting from the continued accretion of plaque and/or thrombi on the displaced occluding deposits.
Laser irradiation has been proposed for the permanent removal of the aforementioned material deposits. The present invention insofar as it applies to laser angioplasty procedures is basically directed to laser irradiation referred to here as the indirect laser irradiation technique and involves the insertion of an optical fiber into the arterial or venous channel to function as a transmissive element for delivery of laser energy to a thermally conductive device disposed at the treatment site. Cooling and temperature control of the probe are of critical importance and constitute primary concerns in the use of such laser-energized devices.
Another primary concern in the use of the aforementioned probe devices is ensuring that the thermally conductive structure is suitably attached to the optical fiber such that it will not become disengaged during use. Federal Republic of Germany Patent No. 2,826,383 published Dec. 20, 1979 as well as two later U.S. patents (U.S. Pat. No. 4,646,737and U.S. Pat. No. 4,662,368) disclose a heat generating element comprising a metal probe body mounted on an optical fiber through which laser energy is transmitted to the probe body to generate heat energy. The German patent discloses cooling of the probe device by flowing a gas or a fluid to extract heat from the heat generating element. While these patents refer to sensing the temperature and in some cases by use of a thermocouple attached to the heat generating element, none of the referred to patents disclose means for both sensing and controlling the temperature of the heat generating element.
The two U.S. patents mentioned in the preceding paragraph do however disclose monitoring probe temperature by monitoring reflected infrared radiation emanating from the laser-energized heated probe after the laser energy source is deactivated. Such a method does not lend itself to real time monitoring or control of probe temperature since the laser is in fact turned off while measurements are made during the cooling cycle of the probe. These probes rely heavily on a dosimetry matrix to estimate probe temperature, with prior in-vitro data having been accumulated in the matrix relating probe temperature to input laser power level. Such a dosimetry matrix is highly variable and dependent upon the fluid dynamic environment surrounding the probe body, resulting in potentially large deviations from predicted probe temperatures. See also an article by George S. Abela et al entitled "Hot Tip: Another Method of Laser Vascular Recanalization" published in Surgery and Medicine 5:327-335, 1985.
The laser energized thermal probe described in commonly-owned U.S. Pat. No. 4,760,845 employs a coiled wire as a means of joining the probe body to the optical fibers and preventing the probe from becoming disengaged during use. This helically wound wire also serves as a means for dissipating heat generated by the probe in use, thereby preventing the heat thus generated from reaching the area where the tip is mechanically attached to the optical fiber jacket and avoiding the need for cooling fluids and the like. A mass of a laser energy-absorptive, thermally conductive, high emissivity medium is contained within the interior of the probe tip to maximize the absorption of the laser energy by the probe.
Prior copending U.S. application Ser. No. 180,188 discloses a thermal probe assembly which comprises means for real time sensing and controlling of the temperature of the heat generating element, and responsively controlling the laser power to maintain some predetermined temperature. Temperature sensing and monitoring has also been accomplished with an element separate from the optical fiber, as described in U.S. Pat. No. 4,476,512.
In electrically heated vascular probes, which typically comprises a large hollow cylinder and an inner heater coil, a thermocouple element may be contained within the heater coil inside the probe tip. Such electrical probes are however characterized by slow response times and limited temperature responsiveness, and inherently require the presence of electrical current at the probe tip site. See the article, "The Heated Probe: A New Endoscopic Method For Stopping Massive Gastrointestinal Bleeding" by Robert L. Protell et al., Gastroenterology 74, pages 257-262 (1978).
Accordingly, it is an object of the present invention to provide a laser-energizable heat probe assembly capable of operating at relatively high temperatures, which does not require the introduction of an externally supplied coolant medium to the treatment site, and possesses a high degree of structural integrity.
A further object of this invention is to provide a thermocouple-equipped laser energizable heated probe assembly in which temperatures are readily monitored via a temperature sensing thermocouple associated with the laser heated probe and coupled to a laser power control system.
A further and significant object of the invention is to provide a probe assembly having improved means for securely attaching the probe body to the optical fiber.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.